1. Field of the Invention
The present invention relates to controlling an effusion cell in a deposition system, and more particularly, to a method of controlling an effusion cell in a deposition system that is capable of preventing a change in the characteristics of a material, the clogging of a nozzle and splashing.
2. Description of the Related Art
An Electro Luminescent Display (ELD) is classified into an Inorganic Electro Luminescent Display (IELD) and an Organic Electro Luminescent Display (OELD) in accordance with the material forming the luminescent layer. The OELD can be driven by low voltage, is lightweight and flat and has a wide angular field and also a rapid response speed. Accordingly, those involved in this field are interested in OELDs.
An organic electro luminescent diode of the OELD is composed of an anode, an organic layer and a cathode formed as a lamination on a substrate. The organic electro luminescent diode includes an organic luminescent layer radiating light through the reunion of a hole and an electron. Also, in the organic electro luminescent diode, an organic electron injecting layer and an electron transporting layer are interposed between the cathode and the organic luminescent layer and an organic hole injecting layer and a hole transporting layer are interposed between the anode and the organic luminescent layer in order to enhance the luminescent efficiency by transmitting holes and electrons to the organic luminescent layer.
The organic electro luminescent diode, which has the above-mentioned structure, is fabricated by physical vapor deposition including a vacuum plating method, an ion plating method and a sputtering method or a chemical vapor deposition dependent upon reaction gases. More particularly, in order to form an organic layer of an organic electro luminescent diode, the vacuum plating method is widely used to deposit evaporated organic material in a vacuum. The vacuum plating method uses an effusion cell to inject evaporated organic material on a substrate within a vacuum chamber.
The effusion cell is composed of a crucible having deposition material dissolved in itself and a heater for heating the crucible. In addition, the effusion cell includes an injection nozzle for injecting an evaporated deposition material and a guiding pathway for guiding an evaporated deposition material from the crucible to the injection nozzle. Accordingly, while a substrate is equipped within vacuum chamber, the deposition material, which is heated by the heater and then evaporated, is injected into the substrate by the injection nozzle via the guiding pathway and then deposited.
But the effusion cell entails the problems of the clogging of an injection nozzle and splashing, etc because a deposition material evaporated in a crucible is liquidized and condensed by the condensation of a guiding pathway or an injection nozzle. In conclusion, a non-uniform injection of the evaporated deposition material through the injection nozzle causes the above problems, and thus uniformity of an organic layer formed on a substrate is difficult.
In addition, when the crucible is heated by a deposition rate control method from the beginning, a temperature of the effusion cell is abruptly increased or an overshoot is excessively generated, thereby causing a change in the characteristics of the material or splashing.